Electrochemical pump

ABSTRACT

In an electrochemical hydrogen pump, an anode separator, an anode diffusion layer, an electrolyte membrane, a cathode diffusion layer and a cathode separator are laminated sequentially, in which the anode separator has a first recess portion that accommodates the anode diffusion layer, and a bottom surface of the first recess portion is a bowl-shaped curved surface having a protruding central portion; the cathode separator has a second recess portion that accommodates the cathode diffusion layer, and a bottom surface of the second recess portion is a bowl-shaped curved surface having a recessed central portion.

TECHNICAL FIELD

The technical field relates to an electrochemical hydrogen pump, and particularly, to an electrochemical hydrogen pump that compresses hydrogen.

BACKGROUND

In recent years, a home fuel cell using hydrogen as fuel has been developed and spread. In addition, similarly to the home fuel cell, mass production and commercial use of a fuel cell vehicle using hydrogen as fuel has started.

The home fuel cell uses existing city gas and existing commercial power, but the fuel cell vehicle requires hydrogen infrastructure. Therefore, it is necessary to expand hydrogen stations as hydrogen infrastructure in order to widely spread the fuel cell vehicle in the future.

However, large-scale equipment and lands are required to construct the hydrogen stations. Accordingly, a huge amount of money is required. This is a big problem that should be solved for the spreading of the fuel cell vehicle.

Therefore, it is desired to develop a small home hydrogen filling device that is compact and inexpensive as an alternative to a large hydrogen station. The most important factor in the development of the small hydrogen filling device is the development of a compressor that compresses hydrogen, and what is currently drawing attention is an electrochemical hydrogen pump capable of electrochemically pressurizing hydrogen.

Compared with a related-art mechanical hydrogen compressing device, the electrochemical hydrogen pump has many merits such as being compact, having high pressurizing efficiency, no need of maintenance due to absence of mechanical operating parts, and having little noise. Therefore, the practical application of the electrochemical hydrogen pump has been desired.

Currently, it is considered to electrochemically compress hydrogen produced by using a fuel reforming device of a home fuel cell by using an electrochemical hydrogen pump.

If such an electrochemical hydrogen pump is used in a small hydrogen filling device, the following merits are presented in addition to the above-described merits. That is, although the concentration of hydrogen produced using the fuel reforming device is about 75%, it is theoretically possible to purify the hydrogen to approximately 100% and to pressurize to an ultra-high pressure at which the hydrogen can be filled in a fuel cell vehicle.

The structure of the electrochemical hydrogen pump is similar to that of a power generation stack of a home fuel cell. A difference from the power generation stack of the home fuel cell is that the pressure of a cathode electrode needs to be ultra-high to allow hydrogen to be filled in the fuel cell vehicle, as compared with an anode electrode that supplies low-pressure hydrogen. Therefore, when the power generation stack of the home fuel cell is used as an electrochemical hydrogen pump, a support structure for an electrolyte membrane interposed between the two electrodes needs to be a special structure.

FIG. 1 is a diagram illustrating a structure of a power generation stack 1 of a related-art fuel cell. As shown in FIG. 1, in the power generation stack 1, respective surfaces of an electrolyte membrane 102, on which an anode electrode layer 103 and a cathode electrode layer 104 are formed, are held between an anode diffusion layer 105 and a cathode diffusion layer 106.

Outer sides of the anode diffusion layer 105 and the cathode diffusion layer 106 are held between an anode separator 107 and a cathode separator 108. Outer sides of the anode separator 107 and the cathode separator 108 are held between an anode insulation plate 111 and a cathode insulation plate 112. Outer sides of the anode insulation plate 111 and the cathode insulation plate 112 are held between an anode endplate 113 and a cathode endplate 114. Further, the anode endplate 113 and the cathode endplate 114 are held between a bolt 115 and a nut 110 while the bolt 115 and the nut 110 are fastened to each other.

A seal 109 is attached around the anode diffusion layer 105 and the cathode diffusion layer 106 so that gas does not leak to the outside. When the power generation stack 1 of the fuel cell is used as a hydrogen pump, an anode inlet 116 is used to supply low-pressure hydrogen, an anode outlet 117 is used to recover excessive low-pressure hydrogen, a cathode inlet 118 is used to take out high-pressure hydrogen, and a cathode outlet 119 is sealed since not being used.

Here, a case where the power generation stack 1 is constituted by one cell including the electrolyte membrane 102, the anode diffusion layer 105, the cathode diffusion layer 106, the anode separator 107, and the cathode separator 108 has been described. However, the power generation stack 1 generally includes a plurality of cells having the above-described structure.

The low-pressure hydrogen is supplied from the anode inlet 116, and a voltage is applied between the anode separator 107 and the cathode separator 108 by a power source 20 in a state where the low-pressure hydrogen flows into a flow path groove 107 a on the anode side. Thereafter, hydrogen is dissociated into protons and electrons in the anode electrode layer 103 as shown in equation (1).

H₂ (low-pressure)→2H⁺+2e⁻  (1)

The protons dissociated in the anode electrode layer 103 move through the electrolyte membrane 102 together with water molecules; the electrons move from the anode diffusion layer 105, pass through the anode separator 107, and then via the power source 20, pass through the cathode separator 108 and the cathode diffusion layer 106 to the cathode electrode layer 104.

On the cathode electrode side, as shown in equation (2), a reduction reaction takes place between protons that have moved through the electrolyte membrane 102 and electrons that have moved from the cathode diffusion layer 106 to produce hydrogen. At this time, the hydrogen gas pressure in a flow path groove 108 a on the cathode side rises when the cathode inlet 118 is sealed, and a high-pressure hydrogen gas is produced.

2H⁺+2e⁻→H₂ (high-pressure)   (2)

Here, a relationship among a hydrogen pressure P1 on the anode side, a hydrogen pressure P2 on the cathode side and a voltage E is expressed by equation (3).

E=(RT/2F)ln(P2/P1)+ir   (3)

In equation (3), a gas constant (8.3145 J/K·mol) is denoted by R, a temperature (K) of the cell constituting the power generation stack 1 by T, a Faraday constant (96485 C/mol) by F, the pressure (MPa) on the cathode side by P2, the pressure (Pa) on the anode side by P1, a current density (A/cm²) by i, and a cell resistance (Ω·cm²) by r.

As can be understood from equation (3), if the voltage is increased, the pressure P2 on the cathode side rises.

FIG. 2A is a perspective view of a related-art anode diffusion layer 105. FIG. 2B is a perspective view of a related-art anode separator 107. FIG. 3 is a perspective view of the related-art anode diffusion layer 105 and the related-art anode separator 107 in a combined state.

In the related-art power generation stack 1, in order to accommodate the anode diffusion layer 105 in a recess portion of the anode separator 107, a gap is required between an outer circumference of the anode diffusion layer 105 and a side surface of the recess portion of the anode separator 107. In order to accommodate the cathode diffusion layer 106 in a recess portion of the cathode separator 108, a gap is required between an outer circumference of the cathode diffusion layer 106 and a side surface of the recess portion of the cathode separator 108.

In order to incorporate the disc-shaped anode diffusion layer 105 having a diameter d as shown in FIG. 2A into the recess portion having an inner diameter D formed in the anode separator 107 shown in FIG. 2B, the inner diameter D is required to be larger than the diameter d. In the case where the inner diameter D of the recess portion is larger than the diameter d of the anode diffusion layer 105, an anode side gap 121 having a width Δ is formed between the outer circumference of the anode diffusion layer 105 and the side surface of the recess portion of the anode separator 107, as shown in FIG. 3. The width Δ of the anode side gap 121 is approximately half the difference between the diameter d and the inner diameter D.

When the anode diffusion layer 105 is 100 mm in diameter, reference dimensions of the diameter d and the inner diameter D are set such that the width Δ of the anode side gap 121 is, for example, about 0.1 mm.

If the difference between the diameter d and the inner diameter D is set to be smaller than 0.1 mm, there is a probability that the size relationship between the diameter d and the inner diameter D is reversed and that the anode diffusion layer 105 cannot be incorporated into the recess portion of the anode separator 107, due to variations in dimensions during manufacturing of the anode diffusion layer 105 and the anode separator 107.

It is also conceivable that when the width Δ of the anode side gap 121 is set to be smaller than 0.1 mm, dimensions of the anode diffusion layer 105 and the anode separator 107 needs to be examined after being manufactured and only qualified ones are used. However, in this case, there is a problem that the yield of the anode diffusion layer 105 and the anode separator 107 decreases and the cost becomes high. Therefore, it is necessary to set the width of the anode side gap 121 between the anode diffusion layer 105 and the anode separator 107 to be about 0.1 mm.

Reference dimensions of a diameter d of the cathode diffusion layer 106 and an inner diameter D of the recess portion of the cathode separator 108 are set, so that the width of a cathode side gap 122 formed between the cathode diffusion layer 106 and the cathode separator 108 is also about 0.1 mm (see FIG. 1).

When the power generation stack 1 of the fuel cell having the anode side gap 121 and the cathode side gap 122 is used as a hydrogen pump for pressurizing hydrogen, the electrolyte membrane 102 is pushed from a high-pressure side (cathode side) to a low-pressure side (anode side) by the pressure of hydrogen applied to the cathode side gap 122 as the pressure on a high-pressure side rises. That is, the electrolyte membrane 102 is deformed in a way of hanging from the cathode side gap 122 on the high-pressure side to the anode side gap 121 on the low-pressure side. When the deformation grows, a crack occurs in the electrolyte membrane 102, and eventually the electrolyte membrane 102 is damaged.

For this reason, the pressure of hydrogen that can be pressurized by using the power generation stack 1 of a typical fuel cell as a hydrogen pump is not very high, and it is insufficient to fill hydrogen to the fuel cell vehicle.

Therefore, there has been proposed a structure that supports an electrolyte membrane such that the electrolyte membrane is not damaged even though there is a pressure difference between a high-pressure side and a low-pressure side when using a power generation stack of a typical fuel cell as a hydrogen pump (Japanese Patent No. 6246203 (Patent Document 1)).

FIG. 4 is a longitudinal sectional view of a related-art electrochemical hydrogen pump 23. In the related-art electrochemical hydrogen pump 23, an anode diffusion layer 205 in a low-pressure area is configured to be wider than a cathode diffusion layer 206 to which a high pressure is applied. For this reason, an anode side gap 221 and a cathode side gap 222 are not disposed at positions facing each other with an electrolyte membrane 202 interposed therebetween.

For this reason, the high rigidity anode diffusion layer 205 on the low-pressure side can support the electrolyte membrane 202 even when the high pressure is applied to the electrolyte membrane 202. Therefore, the electrolyte membrane 202 is not subjected to a bending force or a shearing force that causes damage. Therefore, the electrolyte membrane 202 can be securely supported even though there is a difference between the pressure generated in the anode side gap 221 and the pressure generated in the cathode side gap 222.

SUMMARY

However, in the configuration described in Patent Document 1, only the portion corresponding to the area of the cathode diffusion layer 206 is effectively used for pressurizing hydrogen, and the portion wider than the cathode diffusion layer 206 in the anode diffusion layer 205 is a wasted portion that cannot be effectively used despite being a diffusion layer of a sintered metal compact of Ti which is expensive. Therefore, there is a problem to be solved in reducing the manufacturing cost of the electrochemical hydrogen pump 23.

Further, in recent studies, it has been found that in the above-described configuration, a performance problem is caused by the cathode side gap 222 on the high-pressure side and the anode side gap 221 on the low-pressure side. That is, during the operation of the electrochemical hydrogen pump 23, a part of the high-pressure hydrogen reversely diffuses from the cathode side gap 222 on the high-pressure side to the anode side gap 221 on the low-pressure side, and the pressure of the pressurized hydrogen is decreased. That is, the pressurizing efficiency of the electrochemical hydrogen pump 23 decreases.

Further, it has become clear that the following problems arise when hydrogen is pressurized to fill the fuel cell vehicle. That is, central portions of a cathode separator 208, a cathode insulation plate 212 and a cathode end plate 214 are displaced in a direction of Y1 in FIG. 4 with the rise of the pressure of hydrogen that fills a flow path groove 208 a of the cathode separator 208 and a gap of the cathode diffusion layer 206. Further, central portions of the electrolyte membrane 202, the anode diffusion layer 205, the anode separator 207, an anode insulation plate 211 and an anode end plate 213, are displaced in a direction of Y2.

Accordingly, a problem has been revealed that contact surface pressures between the cathode diffusion layer 206 and a cathode electrode layer 204, and between the cathode diffusion layer 206 and the cathode separator 208, in the vicinity of the center, are lower than that of the surrounding, resulting in an increase in contact resistance and an increase in voltage. Generally, a measure of increasing the thickness of the cathode end plate 214 and the anode end plate 213 to improve the rigidity thereof is generally adopted so as to prevent such a phenomenon. However, such a measure leads to other problems that weights of the members become extremely heavy and that handling of each member becomes difficult.

An object of the disclosure is to provide an electrochemical hydrogen pump that prevents damage to an electrolyte membrane 2 due to a pressure difference between a pressure on an anode side and a pressure on a cathode side without causing a decrease in compression performance and an increase in weight of each member, while a width of an anode diffusion layer and a width of a cathode diffusion layer are made the same so as not to obstruct cost control.

In order to solve the above-described problems, an electrochemical pump of the disclosure includes an anode separator, an anode diffusion layer, an electrolyte membrane, a cathode diffusion layer and a cathode separator laminated sequentially, in which the anode separator has a first recess portion that accommodates the anode diffusion layer, and a bottom surface of the first recess portion is a bowl-shaped curved surface having a protruding central portion; the cathode separator has a second recess portion that accommodates the cathode diffusion layer, and a bottom surface of the second recess portion is a bowl-shaped curved surface having a recessed central portion.

According to the disclosure, an anode side gap between the anode diffusion layer and the anode separator, or a cathode side gap between the cathode diffusion layer and the cathode separator can be eliminated. Therefore, the decrease in the compression performance due to diffusion of concentrated hydrogen from the cathode side gap to the anode side gap through the electrolyte membrane is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for illustrating a structure of a power generation stack of a related-art fuel cell.

FIG. 2A is a perspective view of a related-art anode diffusion layer.

FIG. 2B is a perspective view of a related-art anode separator.

FIG. 3 is a perspective view of the related-art anode diffusion layer and the related-art anode separator in a combined state.

FIG. 4 is a longitudinal sectional view of a related-art electrochemical hydrogen pump.

FIG. 5 is a longitudinal sectional view of an electrochemical hydrogen pump in Embodiment 1.

FIG. 6A is a perspective view of a cross section of an anode diffusion layer in Embodiment 1.

FIG. 6B is a perspective view of a cross section of a cathode diffusion layer in Embodiment 1.

FIG. 7A is a perspective view of a cross section of an anode separator when a flow path groove is not processed.

FIG. 7B is a perspective view of a cross section of the anode separator after the flow path groove is processed.

FIG. 7C is a perspective view of a cross section of a cathode separator when a flow path groove is not processed.

FIG. 7D is a perspective view of a cross section of the cathode separator after the flow path groove is processed.

FIG. 8A is a longitudinal sectional view for illustrating an assembly procedure of the electrochemical hydrogen pump.

FIG. 8B is a longitudinal sectional view for illustrating an assembly procedure of the electrochemical hydrogen pump.

FIG. 9 is a circuit diagram of an evaluation device for an electrochemical hydrogen pump.

FIG. 10 is a diagram for illustrating evaluation results of the electrochemical hydrogen pump.

FIG. 11 is a longitudinal sectional view of an electrochemical hydrogen pump in Embodiment 2.

FIG. 12 is a longitudinal sectional view of an electrochemical hydrogen pump in Embodiment 3.

FIG. 13 is a longitudinal sectional view of an electrochemical hydrogen pump in a comparative example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the disclosure will be described with reference to the drawings.

Embodiment 1

FIG. 5 is a longitudinal sectional view of an electrochemical hydrogen pump 24 in Embodiment 1.

<Overall Configuration>

In the electrochemical hydrogen pump 24 in Embodiment 1, both surfaces of an electrolyte membrane 2 on which an anode electrode layer 3 and a cathode electrode layer 4 are respectively formed are held between an anode diffusion layer 5 and a cathode diffusion layer 6, and outer sides of the anode diffusion layer 5 and the cathode diffusion layer 6 are held between an anode separator 7 and a cathode separator 8.

Further, outer sides of the anode separator 7 and the cathode separator 8 are held between an anode insulation plate 11 and a cathode insulation plate 12, and outer sides of the anode insulation plate 11 and the cathode insulation plate 12 are held between an anode end plate 13 and a cathode end plate 14. Further, the above-mentioned components are pressed by a press machine from outer sides of the anode end plate 13 and the cathode end plate 14 so as to be in close contact with each other.

The pressed state is maintained by bolts 15 and nuts 10. The seal 9 is attached around the anode diffusion layer 5 and the cathode diffusion layer 6 so that gas does not leak to the outside.

The electrolyte membrane 2 is a cation permeable membrane, and Nafion (registered trademark, manufactured by DuPont) and Aciplex (product name, manufactured by Asahi Kasei Corporation), for example, are used for the electrolyte membrane 2. The anode electrode layer 3 including, for example, a RuIrFeOx catalyst, is provided on an anode side surface of the electrolyte membrane 2, and the cathode electrode layer 4 including, for example, a platinum catalyst, is provided on a cathode-side surface of the electrolyte membrane 2.

The anode diffusion layer 5 is required to withstand the pressing of the electrolyte membrane 2 due to high-pressure hydrogen of a flow path groove 8 a in the cathode separator 8. For this reason, a conductive porous body having sufficient rigidity, such as a titanium fiber sintered compact or a titanium powder sintered compact plated with platinum on surfaces thereof, is used as the anode diffusion layer 5.

A porous body, such as a graphitized carbon fiber (for example, performing graphitization by treating carbon fiber at a temperature of 2000° C. or higher), a titanium fiber sintered compact, or a titanium powder sintered compact having high elasticity and plated with platinum on surfaces thereof, is made to be paper-shaped and used as the cathode diffusion layer 6.

A product manufactured by compression molding fluoro-rubber is used as the seal 9. SUS316L plate materials, for example, in which flow path grooves 7 a and 8 a are formed by a cutting process are used as the anode separator 7 and the cathode separator 8.

<Anode Diffusion Layer 5 and Cathode Diffusion Layer 6>

FIG. 6A is a perspective view of a cross section of the anode diffusion layer 5 in Embodiment 1, and FIG. 6B is a perspective view of a cross section of the cathode diffusion layer 6 in Embodiment 1.

As shown in FIG. 6A, the anode diffusion layer 5 is generally formed in a disc shape having a thickness t1 and a diameter d1. A central portion of the disc-shaped anode diffusion layer 5 protrudes in a bowl shape by a dimension α1 when no external force is applied. The anode diffusion layer 5 is formed into such a shape by, for example, deforming a disc that is of a titanium fiber sintered compact or a titanium powder sintered compact plated with platinum on surfaces thereof and that has a thickness t1, using a press molding method. The anode diffusion layer 5 is used within a range of elastic deformation such that even when being deformed due to an external force, the anode diffusion layer 5 can restore to an original shape once the external force is removed.

As shown in FIG. 6B, the cathode diffusion layer 6 is generally formed in a disc shape having a thickness t1 and a diameter d1. When no external force is applied, from an outer circumferential portion to a central portion in FIG. 6B, the disc-shaped cathode diffusion layer 6 protrudes downward by a dimension α2, and then protrudes upward in the vicinity of the center by a dimension α3 in a bowl shape.

An apex of the central bowl shape is positioned lower than the outer circumferential portion by a dimension β. A disc that is of a titanium fiber sintered compact or a titanium powder sintered compact plated with platinum on surfaces thereof and that has a thickness t1, for example, is used as the cathode diffusion layer 6. The cathode diffusion layer 6 is formed into such a shape by using the press molding method. The cathode diffusion layer 6 is used within a range of elastic deformation such that even when being deformed due to an external force, the cathode diffusion layer 6 can restore to an original shape once the external force is removed.

FIG. 7A is a perspective view of a cross section of the anode separator 7 when the flow path groove 7 a is not processed, and FIG. 7B is a perspective view of a cross section of the anode separator 7 after the flow path groove 7 a is processed. FIG. 7C is a perspective view of a cross section of the cathode separator 8 when the flow path groove 8 a is not processed, and FIG. 7D is a perspective view of a cross section of the cathode separator 8 after the flow path groove 8 a is processed.

<Anode Separator 7>

As shown in FIG. 7A, the anode separator 7 is formed in a disc shape having a thickness t2 and a diameter d2. The anode separator 7 has a recess portion 25 for accommodating the anode diffusion layer 5 and having a diameter D1, on a surface in contact with the anode diffusion layer 5. A depth of the recess portion 25 in the vicinity of a side surface is T1. Meanwhile, a central portion of the recess portion 25 is raised by a dimension δ from a bottom surface 25 a adjacent to the side surface. That is, the bottom surface 25 a is a bowl-shaped curved surface.

As shown in FIG. 7B, the meandering flow path groove 7 a in which anode gas (low-pressure hydrogen gas) flows is processed on the bottom surface 25 a of the anode separator 7. Bolt holes 26 through which the bolts 15 are inserted are provided at an outer side of the recess portion 25.

As shown in FIG. 7C, the cathode separator 8 is formed in a disc shape having a thickness t3 and a diameter d2. The cathode separator 8 has a recess portion 27 for accommodating the cathode diffusion layer 6 and having a diameter D1, on a surface in contact with the cathode diffusion layer 6. A depth of the recess portion 27 in the vicinity of a side surface is T1. Meanwhile, a central portion of the recess portion 27 is recessed by a dimension δ from a bottom surface 27 a adjacent to the side surface, and the bottom surface 27 a is a bowl-shaped curved surface.

As shown in FIG. 7D, the meandering flow path groove 8 a in which cathode gas (high-pressure hydrogen gas) flows is processed on the bottom surface 27 a of the cathode separator 8. The bolt holes 26 through which the bolts 15 are inserted and a groove 28 in which the seal 9 is accommodated, are provided at an outer side of the recess portion 27.

It is preferable that the diameter D1 of the recess portion 25 of the anode separator 7 and the diameter D1 of the recess portion 27 of the cathode separator 8 are larger than the diameter d1 of the anode diffusion layer 5 and the diameter d1 of the cathode diffusion layer 6. It is also preferable that the protrusion dimension α1 of the central portion of the anode diffusion layer 5 is larger than the protrusion dimension δ of the surface of the anode separator 7 which is in contact with the anode diffusion layer 5.

It is preferable that an area of a curved surface 29 of the anode diffusion layer 5 which is in contact with the anode separator 7 is larger than an area of the bottom surface 25 a of the recess portion 25 of the anode separator 7 before the flow path groove 7 a is processed, when no external force is applied to the anode diffusion layer 5.

It is preferable that an area of a curved surface 30 of the cathode diffusion layer 6 which is in contact with the cathode separator 8 is larger than an area of the bottom surface 27 a of the recess portion 27 of the cathode separator 8 before the flow path groove 8 a is processed, when no external force is applied to the cathode diffusion layer 6.

It is preferable that the thickness t1 of the anode diffusion layer 5 and the cathode diffusion layer 6 is about 10% thicker than the depth T1 in the vicinity of the side surface of the recess portion 25 of the anode separator 7 and the recess portion 27 of the cathode separator 8.

<Assembly Procedure>

Next, an assembly procedure of the electrochemical hydrogen pump 24 will be described. FIG. 8A and FIG. 8B are longitudinal sectional views illustrating the assembly procedure of the electrochemical hydrogen pump 24.

First, the anode end plate 13 is placed on an assembly table (not shown). The anode insulation plate 11 and the anode separator 7 are laminated thereon. The anode diffusion layer 5 is placed on the anode separator 7, and the electrolyte membrane 2 is laminated thereon. At this time, the anode diffusion layer 5 having the diameter d1 is fitted to an inner side of the recess portion 25 of the anode separator 7 having the diameter D1.

Further, the cathode diffusion layer 6, the cathode separator 8, the cathode insulation plate 12 and the cathode end plate 14 are laminated sequentially on the electrolyte membrane 2. At this time, the seal 9 is fitted into the groove 28 of the cathode separator 8 in advance. The cathode diffusion layer 6 having the diameter d1 is fitted to an inner side of the recess portion 27 of the cathode separator 8 having the diameter D1.

<Compression Operation>

Next, the assembly table (not shown), on which the anode end plate 13 is placed, is installed in a press machine (not shown), and a compression force is applied by pressing the cathode end plate 14 downward toward the assembly table. In a state where the cathode end plate 14 is pressed toward the assembly table, the anode separator 7 and the cathode separator 8 press the anode diffusion layer 5 and the cathode diffusion layer 6 toward the electrolyte membrane 2.

FIG. 8A shows an electrochemical hydrogen pump 24A in a state where no compression force is applied. The anode diffusion layer 5 having the diameter d1 has been fitted to the inner side of the recess portion 25 of the anode separator 7 having the diameter D1. The cathode diffusion layer 6 having the diameter d1 has been fitted to the recess portion 27 of the cathode separator 8 having the diameter D1.

A portion, in the vicinity of the outer circumferential portion, of the curved surface 29 of the anode diffusion layer 5 is in contact with the anode separator 7, but the central portion of the curved surface 29 is not in contact with the anode separator 7. Similarly, a portion, in the vicinity of the outer circumferential portion, of the curved surface 30 of the cathode diffusion layer 6 is in contact with the cathode separator 8, but the central portion of the curved surface 30 is not in contact with the cathode separator 8.

An outer circumferential surface 5 a of the anode diffusion layer 5 is not in contact with a side surface 25 b of the recess portion 25 of the anode separator 7, and an outer circumferential surface 6 a of the cathode diffusion layer 6 is not in contact with a side surface 27 b of the recess portion 27 of the cathode separator 8.

FIG. 8B shows an electrochemical hydrogen pump 24B in a state during the compression. When a compression force is further applied from the state shown in FIG. 8A, the outer circumferential surface 5 a of the anode diffusion layer 5 comes into contact with the side surface 25 b of the recess portion 25 of the anode separator 7, as shown in FIG. 8B. The outer circumferential surface 6 a of the cathode diffusion layer 6 comes into contact with the side surface 27 b of the recess portion 27 of the cathode separator 8.

However, even at this stage, the central portion of the curved surface 29 of the anode diffusion layer 5 is still not in contact with the anode separator 7. Similarly, the central portion of the curved surface 30 of the cathode diffusion layer 6 is not in contact with the cathode separator 8.

Further, when the compression force is further applied as it is, the curved surface 29 of the anode diffusion layer 5 comes into contact with the anode separator 7 entirely as shown in FIG. 5. Similarly, the curved surface 30 of the cathode diffusion layer 6 comes into contact with the cathode separator 8 entirely.

Before the compression force is applied, the area of the curved surface 29 of the anode diffusion layer 5 which is in contact with the anode separator 7 is larger than the area of the bottom surface 25 a of the recess portion 25 before the flow path groove 7 a of the anode separator 7 is processed. In other words, before the compression force is applied, the diameter d1 of the anode diffusion layer 5 is smaller than the diameter D1 of the recess portion 25 of the anode separator 7.

Therefore, at the time of compression, the anode diffusion layer 5 is pressed into the recess portion 25 of the anode separator 7 while being compressed in a direction orthogonal to a thickness direction. In other words, the anode diffusion layer 5 is disposed in the recess portion 25 in a compressed state. Since the outer circumferential surface 5 a of the anode diffusion layer 5 is pressed against the side surface 25 b of the recess portion 25 of the anode separator 7 by the compression force, the anode side gap 221 (see FIG. 4) between the anode diffusion layer 5 and the anode separator 7 can be eliminated. That is, the diameter d1 of the anode diffusion layer 5 is equal to the diameter D1 of the recess portion 25 of the anode separator 7. At this time, the height of the anode diffusion layer 5 is lower than that of the anode diffusion layer 5 before the compression force is applied. The anode diffusion layer 5 is also compressed in the thickness direction, and the thickness thereof becomes the same as the depth T1 in the vicinity of the side surface 25 b of the recess portion 25 of the anode separator 7.

Similarly, before the compression force is applied, the area of the curved surface 30 of the cathode diffusion layer 6 which is in contact with the cathode separator 8 is larger than the area of the bottom surface 27 a of the recess portion 27 of the cathode separator 8 before the flow path groove 8 a is processed. In other words, before the compression force is applied, the diameter d1 of the cathode diffusion layer 6 is smaller than the diameter D1 of the recess portion 27 of the cathode separator 8.

Therefore, the cathode diffusion layer 6 is pressed into the recess portion 27 of the cathode separator 8 while being compressed in a direction orthogonal to a thickness direction. In other words, the cathode diffusion layer 6 is disposed in the recess portion 27 in a compressed state. Since the outer circumferential surface 6 a of the cathode diffusion layer 6 is pressed against the side surface 27 b of the recess portion 27 of the cathode separator 8 by the compression force, the cathode side gap 222 (see FIG. 4) between the cathode diffusion layer 6 and the cathode separator 8 can be eliminated. That is, the diameter d1 of the cathode diffusion layer 6 is equal to the diameter D1 of the recess portion 27 of the cathode separator 8. At this time, the height of the cathode diffusion layer 6 is lower than that of the cathode diffusion layer 6 before the compression force is applied. The cathode diffusion layer 6 is also compressed in the thickness direction, and the thickness thereof becomes the same as the depth T1 in the vicinity of the side surface 27 b of the recess portion 27 of the cathode separator 8.

In such an electrochemical hydrogen pump 24, the electrolyte membrane 2 compresses the anode diffusion layer 5 in the thickness direction (direction of Y2) with the rise of the pressures of hydrogen filled in the flow path groove 8 a and in gaps of the cathode diffusion layer 6. Further, the anode diffusion layer 5 presses a central portion of the anode separator 7 downward (compressing in the direction of Y2). At this time, the pressure of the high-pressure hydrogen acts on the anode diffusion layer 5 in a direction (direction of Y2) in which the anode diffusion layer 5 is close to be a flat plate.

Accordingly, as the pressure of hydrogen rises, a surface pressure between the outer circumferential surface 5 a of the anode diffusion layer 5 and the side surface 25 b of the recess portion 25 of the anode separator 7 rises greatly. Therefore, even when the pressure of hydrogen in the cathode separator 8 is high, a state in which the anode side gap 121 between the anode diffusion layer 5 and the anode separator 7 does not exist can be maintained.

<Evaluation Device>

FIG. 9 is a circuit diagram of an evaluation device 31 for the electrochemical hydrogen pump 24. A power source 120 supplies a current to the electrochemical hydrogen pump 24. A hydrogen cylinder and a regulator 33 supply low-pressure hydrogen to the electrochemical hydrogen pump 24. The low-pressure hydrogen is humidified by a bubbler 34 and a heater 35.

A gas-liquid separation device 36 and a cooling device 37 reduce the dew point of surplus hydrogen not used in the electrochemical hydrogen pump 24. The pressure on a high-pressure side is measured by a pressure gauge 38, and an exhaust valve 39 disposed downstream of the pressure gauge 38 is kept closed at usual times and opened when the pressure is equal to or greater than a predetermined value.

However, a degree to which the exhaust valve 39 is opened is adjusted so that a sufficient pressure loss occurs. That is, the degree to which the exhaust valve 39 is opened is set such that the pressure of hydrogen having passed through the exhaust valve 39 is reduced to approximately the atmospheric pressure (approximately 1.05 times the atmospheric pressure) by the pressure loss occurring at the exhaust valve 39.

The dew point of hydrogen reduced to approximately the atmospheric pressure is lowered by the gas-liquid separation device 36 and the cooling device 37. The hydrogen whose pressure has been reduced is diluted in a dilution device 41 by nitrogen supplied from a nitrogen cylinder 40, and then discharged to an exhaust port 42 leading to the outside.

In the subsequent evaluation process, a temperature of the heater 35 is set to 65° C., and a temperature of the cooling device 37 is set to 20° C.

<Evaluation Process>

A process for evaluating the electrochemical hydrogen pump 24 will be described.

(1) As shown in FIG. 9, the electrochemical hydrogen pump 24 in Embodiment 1 is connected to the evaluation device 31.

(2) A three-way valve 43 is switched from an atmosphere opening position (arrow A) to a closed side (arrow B).

(3) A valve 44 of the nitrogen cylinder 40 for dilution is operated to allow the nitrogen to flow into the dilution device 41.

(4) A valve 45 of the hydrogen cylinder 32 and the regulator 33 are operated to supply low-pressure (pressure ratio of 0.05) hydrogen to the electrochemical hydrogen pump 24. The pressure ratio is a ratio of an actually applied pressure to a predetermined pressure.

(5) The power source 120 is turned ON, and an electrode area is calculated to set a current value such that a current density is 1.0 (A/cm²).

(6) Voltages displayed at the power source 120 are recorded every time the pressure ratio increases by 0.05 until the pressure displayed by the pressure gauge 38 reaches a target pressure (pressure ratio of 1.0).

(7) The power source 120 is turned OFF, and each valve is operated to stop the supply of hydrogen, and then a supply of nitrogen for dilution is stopped.

(8) Finally, the three-way valve 43 is switched from the closed position (arrow B) to the atmosphere opening side (arrow A).

(9) The electrochemical hydrogen pump 24 in Embodiment 1 is removed.

<Evaluation Result>

FIG. 10 is a diagram for illustrating evaluation results of the electrochemical hydrogen pump 24. In FIG. 10, the horizontal axis represents the pressure ratio and the vertical axis represents the voltage ratio. In FIG. 10, a represents an evaluation result of the related-art electrochemical hydrogen pump 23 described in Patent Document 1. In FIG. 10, b represents an evaluation result of the electrochemical hydrogen pump 24 in Embodiment 1. The voltage ratio is a ratio of an actually applied voltage to a predetermined reference voltage.

In the related-art electrochemical hydrogen pump 23 described in Patent Document 1, the voltage ratio gradually increases from a pressure ratio of 0.05 to a pressure ratio of 0.6, and the voltage ratio increases rapidly from the pressure ratio of 0.6 to a pressure ratio of 1.0. In the electrochemical hydrogen pump 24 in Embodiment 1, the voltage ratio gradually increases until the pressure ratio reaches 0.6, and then the voltage ratio increases rapidly. This tendency of the electrochemical hydrogen pump 24 is the same as that of the related-art electrochemical hydrogen pump 23.

However, the voltage ratio of the electrochemical hydrogen pump in Embodiment 1 is lower than that of the related-art electrochemical hydrogen pump 23 by about 0.2 points in a range of the pressure ratio from 0.05 to 0.6, and the performance is improved. In a range of the pressure ratio from 0.6 to 1.0, the difference between the voltage ratio of the electrochemical hydrogen pump 24 in Embodiment 1 and the voltage ratio of the related-art electrochemical hydrogen pump 23 is expanded. That is, when the electrochemical hydrogen pump 24 in Embodiment 1 and the related-art electrochemical hydrogen pump 23 are compared, it can be said that the performance of the electrochemical hydrogen pump 24 is particularly improved when the pressure on the cathode side rises.

The reason why the voltage ratio of the related-art electrochemical hydrogen pump 23 is higher is considered to be the diffusion of concentrated hydrogen from the cathode side gap 222 toward the anode side gap 221 in the electrochemical hydrogen pump 23. That is, the performance of the electrochemical hydrogen pump 24 in Embodiment 1 is improved since improvement has been made in that point.

In FIG. 10, c represents data indicating an evaluation result of an electrochemical hydrogen pump according to Embodiment 2. This will be described below.

Embodiment 2

FIG. 11 is a longitudinal sectional view of an electrochemical hydrogen pump 46 in Embodiment 2. FIG. 11 shows the electrochemical hydrogen pump 46 during assembly before a compression force is applied. A state of the electrochemical hydrogen pump 46 in Embodiment 2 after the assembly is the same with the electrochemical hydrogen pump 24 in Embodiment 1.

<Overall Configuration>

In the electrochemical hydrogen pump 46, since high-pressure hydrogen needs to be stored on a cathode side, the following problems arise. That is, central portions of a cathode end plate 14, a cathode insulation plate 12 and a cathode separator 8 are displaced upward (direction of Y1) in FIG. 11, with the rise of a pressure of hydrogen filling a flow path groove 8 a of the cathode separator 8 and gaps of a cathode diffusion layer 6. Further, central portions of an electrolyte membrane 2, an anode diffusion layer 5, an anode separator 7, an anode insulation plate 11 and an anode end plate 13 are displaced downward (direction of Y2) in FIG. 11.

Since contact surface pressures between the cathode diffusion layer 6 and a cathode electrode layer 4, and between the cathode diffusion layer 6 and the cathode separator 8, in the vicinity of the center, are lower than that of the surrounding due to the displacement, the contact resistance increases and the voltage rises. As a result, the performance of an electrochemical hydrogen pump decreases.

It is considered that this is the reason why the voltage ratio increases rapidly from a pressure ratio of 0.6 to a pressure ratio of 1.0 in the evaluation results of the electrochemical hydrogen pump 23 in Patent Document 1 and the electrochemical hydrogen pump 24 in Embodiment 1 as shown in FIG. 10.

Generally, a measure of increasing the thickness of the cathode end plate 14 and the anode end plate 13 to improve the rigidity thereof is generally adopted so as not to affect the performance by the displacement. However, such a measure leads to other problems that weights of the members become extremely heavy and that handling of each member becomes difficult.

Therefore, in the electrochemical hydrogen pump 46 in Embodiment 2, the cathode diffusion layer 6 is formed to be thicker at the center thereof.

A thickness of an outer circumferential portion of the cathode diffusion layer 6 is t1, and a thickness of the central portion is t4 (t1<t4). For example, t4 is 1.05 times of t1. Accordingly, the contact surface pressures between the cathode diffusion layer 6 and the cathode electrode layer 4, and between the cathode diffusion layer 6 and the cathode separator 8 become larger at the central portion of the cathode diffusion layer 6.

Therefore, even in a case where each component displaces in the direction of Y1 and the direction of Y2 with the rise of the pressure of hydrogen on the cathode side, the contact surface pressures between the cathode diffusion layer 6 and the cathode separator 8, and between the cathode diffusion layer 6 and the cathode electrode layer 4 can be substantially the same at the outer circumferential portion and the central portion of the cathode diffusion layer 6. Therefore, the performance of the electrochemical hydrogen pump 46 does not decrease. That is, decrease in performance of the electrochemical hydrogen pump 46 can be prevented without increasing the thickness of the cathode end plate 14 and the anode end plate 13.

<Evaluation>

In FIG. 10, c represents an evaluation result of the electrochemical hydrogen pump 46 in Embodiment 2.

As shown in FIG. 10, although the electrochemical hydrogen pump 46 in Embodiment 2 has a slight increase in the voltage ratio over the entire range of the pressure ratio from 0.05 to 1.0, an abrupt increase in the voltage ratio is not observed.

It is because a decrease in the contact surface pressures between the cathode diffusion layer 6 and the cathode separator 8, and between the cathode diffusion layer 6 and the cathode electrode layer 4 is prevented as compared with that in Embodiment 1 even when the pressure of hydrogen on the cathode side rises.

That is, in the electrochemical hydrogen pump 46 in Embodiment 2, there is no need to increase the thickness of the cathode endplate 14 and the anode end plate 13.

Embodiment 3

FIG. 12 is a longitudinal sectional view of the electrochemical hydrogen pump 46 in Embodiment 3. FIG. 12 shows the electrochemical hydrogen pump 46 after being assembled. FIG. 13 is a longitudinal sectional view of an electrochemical hydrogen pump in a comparative example.

<Overall Configuration>

In Embodiment 1, as shown in FIG. 5, the side surface 25 b (FIG. 8B) of the recess portion of the anode separator 7 and the outer circumferential surface 5 a (FIG. 8A) of the anode diffusion layer 5 are manufactured to be in close contact with each other. However, due to variations in manufacturing the anode separator 7 and the anode diffusion layer 5, as shown in FIG. 13, an anode side gap 321 may occur on aside of the electrolyte membrane 2 between the side surface 25 b of the recess portion of the anode separator 7 and the outer circumferential surface 5 a of the anode diffusion layer 5. When such an anode side gap 321 occurs, the electrolyte membrane 2 hangs into the anode side gap 321, which eventually leads to breakage of the electrolyte membrane 2 with the rise of the pressure of hydrogen on the cathode side.

Therefore, as shown in FIG. 12, in the electrochemical hydrogen pump 46 in Embodiment 3, the side surface 25 b of the recess portion 25 of the anode separator 7 and the outer circumferential surface 5 a of the anode diffusion layer 5 are inclined with respect to the compression direction, thereby generating an anode side gap 421 on a side opposite to the electrolyte membrane 2, in the vicinity of the contact portion of the side surface 25 b of the recess portion of the anode separator 7 and the outer circumferential surface 5 a of the anode diffusion layer 5.

Accordingly, on a side of the electrolyte membrane 2, the side surface 25 b of the recess portion 25 of the anode separator 7 and the outer circumferential surface 5 a of the anode diffusion layer 5 are reliably brought into close contact in a ridge line of the anode diffusion layer 5 on the side of the electrolyte membrane 2. According to this configuration, even if there are variations in manufacturing, the outer circumferential surface 5 a of the anode diffusion layer 5 can be reliably brought into close contact with the side surface 25 b of the recess portion of the anode separator 7 on the side of the electrolyte membrane 2, so that the electrolyte membrane 2 can be prevented from hanging down in a skimmer even when the pressure of hydrogen on the cathode side is high.

<Evaluation>

In FIG. 10, e represents an evaluation result of the electrochemical hydrogen pump 46 in Embodiment 3. As shown in FIG. 10, the electrochemical hydrogen pump 46 in Embodiment 3 is higher in voltage than the electrochemical hydrogen pump 46 in Embodiment 2 as the pressure ratio approaches 1. It is because the electrolyte membrane 2 pushes the anode diffusion layer 5 in a direction opposite to the electrolyte membrane 2 as the pressure of hydrogen in the cathode rises, causing the anode diffusion layer 5 to be slightly recessed and the contact resistance between the electrolyte membrane 2 and the cathode diffusion layer 6 increased. However, the voltage rises slightly, and there is no problem in practical use.

The electrochemical hydrogen pump of the disclosure has the following characteristics.

An anode diffusion layer 5 is generally disc-shaped, and a central portion thereof protrudes in a bowl shape when no external force is applied.

A cathode diffusion layer 6 is generally disc-shaped, and protrudes in a thickness direction, from an end portion toward a central portion thereof, and then protrudes in an opposite direction to a bowl shape in the vicinity of the center when no external force is applied. An apex of the central bowl shape is positioned lower than an outer circumferential portion.

An anode separator 7 is generally disc-shaped. A surface of the anode separator 7 in contact with the anode diffusion layer 5 has a recess portion 25 that accommodates the anode diffusion layer 5. A depth of the recess portion 25 is not constant, and a bottom surface 25 a is a bowl-shaped curved surface having a protruding central portion.

A cathode separator 8 is generally disc-shaped. A surface of the cathode separator 8 in contact with the cathode diffusion layer 6 has a recess portion 27 that accommodates the cathode diffusion layer 6. A depth of the recess portion 27 is not fixed, and a bottom surface 27 a is a bowl-shaped curved surface having a recessed central portion.

An area of a curved surface 29 of the anode diffusion layer 5 which is in contact with the anode separator 7 is larger than an area of the bottom surface 25 a of the recess portion 25 of the anode separator 7 before a flow path groove 7 a is processed.

An area of a curved surface 30 of the cathode diffusion layer 6 which is in contact with the cathode separator 8 is larger than an area of the bottom surface 27 a of the recess portion 27 of the cathode separator 8 before a flow path groove 8 a is processed.

Further, the thickness of the anode diffusion layer 5 or the cathode diffusion layer 6 is increased from the outer circumferential portion to the center thereof. In the vicinity of a contact portion between a side surface 25 b of the recess portion 25 of the anode separator 7 and the outer circumferential surface 5 a of the anode diffusion layer 5, there is an anode side gap 421 on a side opposite to the electrolyte membrane 2.

According to the above-described characteristics, there are no gaps between the anode diffusion layer 5 and the anode separator 7, and between the cathode diffusion layer 6 and the cathode separator 8, and the electrolyte membrane 2 is not exposed to hydrogen. Therefore, decrease in performance of the electrochemical hydrogen pump due to diffusion of concentrated hydrogen from a high-pressure side to a low-pressure side is prevented.

Further, even when the pressure of hydrogen on a cathode side rises, a decrease in contact surface pressures between the cathode diffusion layer 6 and the cathode separator 8, as well as in contact surface pressures between the cathode diffusion layer 6 and the cathode electrode layer 4 is prevented. Accordingly, the electrochemical hydrogen pump of the disclosure is optimal as a hydrogen compressing device for a small home hydrogen filling device.

The electrochemical hydrogen pump of the disclosure can be used as a hydrogen compressing device for a hydrogen filling device. Further, the structure of the electrochemical hydrogen pump of the disclosure can be used as an electrochemical water electrolysis device which produces hydrogen and oxygen by electrolysis of water. 

What is claimed is:
 1. An electrochemical pump comprising: an anode separator, an anode diffusion layer, an electrolyte membrane, a cathode diffusion layer, and a cathode separator laminated sequentially, wherein the anode separator has a first recess portion that accommodates the anode diffusion layer, and a bottom surface of the first recess portion is a bowl-shaped curved surface having a protruding central portion, and wherein the cathode separator has a second recess portion that accommodates the cathode diffusion layer, and a bottom surface of the second recess portion is a bowl-shaped curved surface having a recessed central portion.
 2. The electrochemical pump according to claim 1, wherein the first recess portion has a flow path groove through which gas flows, and wherein the second recess portion has a flow path groove through which gas flows.
 3. The electrochemical pump according to claim 1, wherein the anode diffusion layer is disposed in the first recess portion in a pressed state, and wherein the cathode diffusion layer is disposed in the second recess portion in a pressed state.
 4. The electrochemical pump according to claim 1, wherein a central portion of the anode diffusion layer protrudes in a bowl shape in a state where no external force is applied, and wherein the cathode diffusion layer protrudes in a thickness direction, from an outer circumferential portion toward a central portion thereof, and further protrudes in an opposite direction toward the central portion in a bowl shape in a state where no external force is applied.
 5. The electrochemical pump according to claim 2, wherein an area of a curved surface of the anode diffusion layer which is in contact with the anode separator is larger than an area of the curved surface of the anode separator before the flow path groove is processed in a state where no external force is applied to the anode diffusion layer, and wherein an area of a curved surface of the cathode diffusion layer which is in contact with the cathode separator is larger than an area of the curved surface of the cathode separator before the flow path groove is processed in a state where no external force is applied to the cathode diffusion layer.
 6. The electrochemical pump according to claim 1, wherein a thickness of the anode diffusion layer or the cathode diffusion layer is increased from an outer circumferential portion to a central portion.
 7. An electrochemical pump comprising: an electrolyte membrane; a pair of plate-shaped diffusion layers disposed to be adjacent to both surfaces of the electrolyte membrane; and a pair of separators, each including a recess portion that accommodates one of the diffusion layers and pressing the one diffusion layer accommodated in the recess portion toward the electrolyte membrane, wherein a diameter of the one diffusion layer is smaller than a diameter of the respective recess portion in a state of not being pressed by the respective separator, and is equal to the diameter of the respective recess portion in a state of being pressed by the separator, and wherein a height of the one diffusion layer in a state of being pressed by the respective separator is lower than a height of the one diffusion layer in a state of not being pressed by the separator.
 8. The electrochemical pump according to claim 7, wherein a central portion of the one diffusion layer is thicker than an outer circumferential portion of the one diffusion layer in a state of not being pressed by the respective separator.
 9. The electrochemical pump according to claim 1, wherein a side surface of the first recess portion of the anode separator and a side surface of the anode diffusion layer are inclined with respect to a laminating direction at a contact portion between the anode separator and the side surface of the anode diffusion layer, so as to make room on an opposite side to the electrolyte membrane. 